a few grains Morton's salt
Grate the chocolate into a saucepan. Add the sugar and cornstarch and mix well. Stir in the boiling water. Cook and stir until thick and smooth. Add the remaining ingredients and beat thoroughly.
The Fanny Farmer Cookbook
"Sicilian Cassata Frosting"
12 oz. Hershey's or Nestlé's semisweet chocolate morsels
1/2 lb. chilled Fleischmann's unsalted margarine, but into bits
Melt the chocolate and coffee together. Cool slightly, then beat in the ice-cold margarine, bit by bit (a food processor makes it easy and quick). Chill until thick enough to spread.
Private Collections: A Culinary Treasure, Ed. J. E. C. Wurtzburger and M. K. Griswold. Walters Art Gallery, Baltimore.